What does Status_quantity in yfs_order_line_status or yfs_order_release_status mean?

Resolving The Problem

The yfs_order_line_status table keeps track of how much quantity (status_quantity) is in a particular status (status) for a given order line. Similarly the yfs_order_release_status table tracks this in higer versions.
As an order transistions from one status to another the status_quantity in one status goes down to 0 and the other one increases until the order line is completely shipped or cancelled. I am quite surprised that this was not conveyed during implementation. Your Sys Admin Guide will tell you what the various status that are being used at your site mean including if they are custom. You will be able to find this from the Admin console - Common Codes section as well.
Some commonly used statuses are 1200- Verified, 1400 - Backordered from Node, 3200 - Sent to Node, 3300 - Being Picked, 3700 - Shipped 4200 - Being returned or some thing along those lines. 0 in the status_quantity means that are no units in that status which should be the case for most old orders for they should be shipped or returned or cancelled.